Lleyton Hewitt rolled back the years to send sixth seed Juan Martin del Potro crashing out of the US Open.

Del Potro, who won the title at Flushing Meadows in 2009, recently pushed Novak Djokovic all the way in the Wimbledon semi-finals and was tipped by many as the man most likely to challenge the Serb, Rafael Nadal and Andy Murray.

But he ran into an inspired Hewitt, himself a former champion, who fought back from two sets to one down to complete a memorable upset in four hours and three minutes.

"I was pumped up when I won my first-round match because I knew I would be playing del Potro and it was a great opportunity to play on (Arthur) Ashe (Stadium)," Hewitt said.

"I don't know how many years I've got left in me, I keep getting asked that question. I just wanted to get out here and put on a great show.

Fun

"A couple of years ago I had a couple of foot surgeries and I didn't know if I would play tennis again. For me to be out here competing, it's a lot of fun. This is why I still play, to have moments like this."

Del Potro looked to have taken a decisive stranglehold on the match when he won the third set after Hewitt had served for a two-set lead.

The 32-year-old served for the fourth set as well, but he also squandered that opportunity before coming through to win what he later described as "one of the the best tie-breaks of my life".

Del Potro had been pushed hard by Guillermo Garcia-Lopez in the first round and he could not handle the energy of Hewitt in the fifth set, with the Argentinian double-faulting on the second match point.

Hewitt, now ranked 66th, has played some vintage stuff in patches in recent years but has not been beyond the fourth round at a grand slam since Wimbledon in 2009.